The present disclosure relates to nickel based superalloy materials and, more particularly, to the preparation of a nickel based superalloy in which the coarse precipitate structure facilitates wrought processes and precipitation hardening is not re-invoked.
Nickel based superalloys are widely used in gas turbine engines such as in turbine rotor disks. The property requirements for such rotor disk materials have increased with the general progression in engine performance. Early engines utilized relatively easily forged steel and steel derivative alloys as the rotor disk materials. These were then supplanted by first generation nickel based superalloys, such as age hardening austenitic (face-centered cubic) nickel-based superalloys, which were capable of being forged, albeit often with some difficulty.
Nickel based superalloys derive much of their strength from the gamma prime [Ni3(Al,X)] phase. The trend has been toward an increase in the gamma prime volume fraction for increased strength. The nickel based superalloy used in the early disk alloys contain about 25% by volume of the gamma prime phase, whereas more recently developed disk alloys contain about 40-70%.
Alloys containing relatively high volume fractions of the gamma prime precipitates, however, is not considered readily amenable to wrought processes such as rolling, swaging, forging, extrusion and variants thereof, unless the material has a fine grain structure. Alloys with coarse grain structure, or single crystal structures, are thus over-aged to coarsen the precipitates, and then some amount of warm working is imparted to the resulting softened material. However, even where practiced, it is conventionally believed that the resulting material may not have sufficient strength and it is absolutely necessary to re-solution all the gamma prime precipitates in the material and perform precipitation heat treatment to achieve reasonable strength.
Currently, solid solution hardened or low gamma prime (γ′) volume fraction alloys are utilized for most high strength applications as the wrought processing pathway for precipitation hardened alloys is considered relatively difficult and expensive.